Valve straightening?

Valver · World Chat Champion Joined: 31 Jan 2005 Karma :

Hi,

Anyone have much experience with straightening valves?

Tomorrow morning i'm going to have a go at straightening my two inlet valves. I'm not sure what kind of tolerances i'm dealing with though? Any ideas? I'm a cheapskate and can't afford £108 each right now.

Any help would be much appreciated!

Cheers!

tonyyzf · Brolly Dolly Joined: 13 May 2005 Karma :

I have done it a long time ago, depends how bad they are though. Once you get them straight you'll have to grind them in using grinding paste and elbow grease.

Valver · World Chat Champion Joined: 31 Jan 2005 Karma :

Cheers Tony Thumbs Up

They arn't too bad but you can see a 3/4degree bend at the bottom of each. Are we talking getting them straight to 10 thou or less? or would straight 'by eye' do?

As for grinding them in, i've got a budding bike mechanic student waiting to do that for me.

tonyyzf · Brolly Dolly Joined: 13 May 2005 Karma :

I just did it by eye, if they look straight when you spin them or when you put them back in their seats then you're not far out.
How did they get bent?

0ddball · World Chat Champion Joined: 15 Jul 2005 Karma :

£108 each? are they gold plated titanium ones? Generally valves are around £15 each.

Valver · World Chat Champion Joined: 31 Jan 2005 Karma :

Husqvarna motard mate Confused

Nightmare busting anything on this bike! I found some second hand ones on the Talsinracing site for £25 each but they were sold by the time i got round to phoning. Huskysport charge £108.10 and Talsin do them for about £1 less.

What happened? Well..................
I had just put a new bearing in the clutch and was fitting the basket bolts when i slightley over tightened one Shocked

It had started to shear but seemed solid enough. Took the bike out for a quick burst and after about 20miles and at about 90mph.....WhrrrrrrrrrrrrrrBang! Back wheel locked up. It looks like the head of the sheared bolt and the washer behind it found there way to the cam chain, forcing it off the lower sprocket. Outcome - Two bent valves and slight heat scars in the barrel.

0ddball · World Chat Champion Joined: 15 Jul 2005 Karma :

Ideally you need to spin them in a lathe. If you turn them at about 1000rpm and they look ok then they generally will be. You could also use a decent electric drill at a push.

If the actual valve head is bent in relation to the stem it's probable some fatigue has already occured and tbh i wouldn't use the valves again unless i had no other choice. Then again, i certainly wouldn't pay over 200 spoons for a new pair.

I'd get in touch with a valve specialist and see what they say. Valves are valves so if you can send one to one of these specialists they can either crack test it and straighten it or even measure it's dimensions and radii and either supply an equivelent off the shelf one or spin a custom one up. Almost certainly for much less than £216.

Valver · World Chat Champion Joined: 31 Jan 2005 Karma :

I'm gonna bend it straight. Turn it in a lathe and check with a micrometer and then Dye penetrant test it. I can do all that at work in the morning. Just don't know how perfect it needs to be.

tonyyzf · Brolly Dolly Joined: 13 May 2005 Karma :

Close enough to get a good seal after grinding in, if I can get it with an electric drill and a hammer then you'll have no probs with the equipment you have to hand, good luck.

Valver · World Chat Champion Joined: 31 Jan 2005 Karma :

I phoned around a few engineering companys this morning and everyone i've spoken to has told me that impact straightening (ie with a hammer would excessively weaken the valve stem and may cause the base to shatter. Also advised that if the valve stem might stick or worse still cause massive power loss if the valve isn't seating perfectly. I've been warned of heat straightening too Sad

Hmmmmm....